Dynamical behavior of higher harmonic generation from a picosecond laser produced solid surface plasma

We have investigated the efficiency of the fifth order harmonics from solid surface plasma by varying the electron density gradient using two 2.2 ps, 1054 nm laser pulses. A 5 ps time difference between the prepulse and main pulse results in an increase in the harmonic signal by a factor of 2–3, which then decreases for time delays greater than 10 ps. Experiments and calculations are presented that demonstrate a strong dependence of the conversion efficiency on the plasma scale length.